The present invention relates generally to document authentication, and more specifically, to identification and authentication of documents in both digital and analog formats, including hard copies of documents.
A variety of approaches may be used to identify the source of a document; however, many approaches do not survive conversions between electronic (digital) format and analog (e.g., hardcopy) format. For example, electronic documents may include digital signatures that can be delivered along with the documents. The recipients of the documents can validate the electronic documents using the digital signatures. Since the digital signatures are delivered with the documents, the recipients know that the documents have been signed.
Another approach to identifying the source of a document is intentional injection of false information into the document, such as inclusion of intentionally misspelled words or false entries in a directory. Presence of the erroneous or false information can be used as identifiers about the origin of the document. The document recipient is usually not aware of the false information, which is easily detected and only contains information about the creator.
A further approach to identifying source information is electronic image modification to embed hidden information. For instance, steganography allows for injection of information into an electronic image without significantly altering image quality and can be used to tag the image. Note that printing the encoded image results in losing the hidden information. Thus, the information does not survive digital-to-analog (printing) and subsequent analog-to-digital (scanning) conversion processes.
An additional identification encoding technique includes tagging printouts with watermarks. For example, printers can be designed to print information about the printer, such as a serial number in a light yellow color and in a very small font that is not visible to the naked eye. However, this information typically does not survive the analog-to-digital (scanning) conversion process.